Epidemiology

1. Epidemiology

2. Epidemiology • Comes from Greek words • epi, meaning “on or upon” • demos,meaning “people” • logos, meaning “the study of” • Study of distribution and determinants of health-related conditions or events in populations

3. History • Hippocrates (circa 400 B.C.) attempted to explain disease occurrence from a rational instead of a supernatural viewpoint

4. John Graunt, a London haberdasher, published his landmark analysis of mortality data in 1662. He was the first to quantify patterns of birth, death, and disease occurrence, noting male-female disparities, high infant mortality, and seasonal variations

5. Mid 1800’s • William Farr began to systematically collect and analyze Britain’s mortality statistics. • John Snow, an anesthesiologist, conducted a series of investigations in London that later earned him the title “the father of epidemiology.”

6. discipline did not flourish until the end of the Second World War

7. Uses

8. Population or community health assessment • What are the actual and potential health problems in the community? • Where are they? • Who is at risk? • Which problems are declining over time? • Which ones are increasing or have the potential to increase? • How do these patterns relate to the level and distribution of services available?

9. The Epidemiologic Approach • Case Definition – a set of standard criteria for deciding whether a person has a particular disease or other health-related condition.

10. Statistics and Reports • When physicians diagnose a case of a reportable disease they send a report of the case to their local health department. • Time - when the case occurred • place - where the patient lived • person - the age, race, and sex of the patient

11. Health departments convert the case counts into rates, which relate the number of cases to the size of the population where they occurred

12. Types of Epidemiology

13. Descriptive Epidemiology • organize and summarize data according to time, place, and person • Time – disease rates change over time – the seasonal increase in influenza with the onset of cold weather • time data is usually shown on a graph

14. Place - describe a health event by place to gain insight into the geographical extent of the problem. • Residence • Birthplace • place of employment • school district • hospital unit, etc

15. Person • inherent characteristics of people • Age • Race • Sex

16. Acquired Characteristics • Immunity • Marital status

17. Activities • Occupation • Leisure activities • Use of medications/tobacco/drugs

18. Conditions under which people live • Socioeconomic status • Access to medical care

19. Analytic Epidemiology • Used to search for causes and effects, or the why and the how.

20. Experimental • determine the exposure status for each individual (clinical trial) or community (community trial); we then follow the individuals or communities to detect the effects of the exposure

21. Observational • observe the exposure and outcome status of each study participant • cohort study - categorize subjects on the basis of their exposure and then observe them to see if they develop the health conditions being studied • case-control study - enroll a group of people with disease (“cases”) and a group without disease (“controls”) and compare their patterns of previous exposures

22. Causation

23. cause of disease is a factor (characteristic, behavior, event, etc.) that influences the occurrence of disease • An increase in the factors leads to an increase in disease. • Reduction of the factors leads to a reduction in disease

24. Agent Environment Host Epidemiologic triangle • traditional model of infectious disease causation.

25. Agent Environment Host Agent • Infectious microorganism - must be present for disease to occur • Virus • Bacterium • Parasite • other microbe

26. Agent Environment Host Host factors • Intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent. • Age • Race • Sex • socioeconomic status • behaviors

27. Agent Environment Host Environmental factors • Extrinsic factors which affect the agent and the opportunity for exposure • physical factors • biologic factors • socioeconomic factors

28. Epidemiology and Disease

29. Mode of Transmission Susceptible Host Reservoir Mode of Transmission Chain of Infection

30. Chain of Infection • reservoir of an agent is the habitat in which an infectious agent normally lives, grows, and multiplies. • Portal of exit is the path by which an agent leaves the source host

31. Chain of Infection • Modes of transmission • Direct – immediate transfer of the agent from a reservoir to a susceptible host by direct contact or droplet spread • Direct contact • Droplet spread • Indirect – an agent is carried from a reservoir to a susceptible host by suspended air particles or by animate (vector) or inanimate (vehicle) intermediaries • Airborne • Vehicleborne • Vectorborne • Mechanical • Biologic

32. Chain of Infection • Portal of entry – means by which an agent enters a susceptible host • Host – individual infected with the agent

33. Increasing amount of disease Pandemic Epidemic Endemic Sporatic Epidemic Disease Occurrence • Level of Disease - amount of a particular disease that is usually present in a community

34. Sporadic - irregular pattern of occurrence, with occasional cases occurring at irregular intervals

35. Endemic - persistent level of occurrence with a low to moderate disease level

36. Epidemic or Outbreak- occurrence of a disease within an area is clearly in excess of the expected level for a given time period

37. Pandemic - an epidemic spreads over several countries or continents, affecting a large number of people